lt3080-1 Linear Technology Corporation, lt3080-1 Datasheet - Page 11

• Manufacturer Part Number: lt3080-1
• Description: Parallelable 1.1a Adjustable Single Resistor Low Dropout Regulator
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
better than 90 percent equalized sharing of the current.
The internal resistance of 25 milliohms (per device) only
adds about 25 millivolts of output regulation drop at an
output of 2A. At low output voltage, 1V, this adds 2.5%
regulation. The output can be set 19mV high for lower
absolute error ±1.3%. Of course, more than two LT3080-1’s
can be paralleled for even higher output current. They are
spread out on the PC board, spreading the heat. Input
resistors can further spread the heat if the input-to-output
difference is high.
Thermal Performance
In this example, two LT3080-1 3mm × 3mm DFN devices
are mounted on a 1oz copper 4-layer PC board. They are
placed approximately 1.5 inches apart and the board is
mounted vertically for convection cooling. Two tests were
set up to measure the cooling performance and current
sharing of these devices.
The fi rst test was done with approximately 0.7V input-
to-output and 1A per device. This gave a 700 milliwatt
dissipation in each device and a 2A output current. The
temperature rise above ambient is approximately 28°C
and both devices were within plus or minus 1°C. Both the
thermal and electrical sharing of these devices is excel-
lent. The thermograph in Figure 5 shows the temperature
distribution between these devices and the PC board
Figure 5. Temperature Rise at 700mW Dissipation
reaches ambient temperature within about a half an inch
from the devices.
The power is then increased with 1.7V across each device.
This gives 1.7 watts dissipation in each device and a device
temperature of about 90°C, about 65°C above ambient
as shown in Figure 6. Again, the temperature matching
between the devices is within 2°C, showing excellent
tracking between the devices. The board temperature has
reached approximately 40°C within about 0.75 inches of
each device.
While 90°C is an acceptable operating temperature for
these devices, this is in 25°C ambient. For higher am-
bients, the temperature must be controlled to prevent
device temperature from exceeding 125°C. A three meter
per second airfl ow across the devices will decrease the
device temperature about 20°C providing a margin for
higher operating ambient temperatures.
Both at low power and relatively high power levels de-
vices can be paralleled for higher output current. Current
sharing and thermal sharing is excellent, showing that
acceptable operation can be had while keeping the peak
temperatures below excessive operating temperatures on
a board. This technique allows higher operating current
linear regulation to be used in systems where it could
never be used before.
Figure 6. Temperature Rise at 1.7W Dissipation
LT3080-1
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